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Q.My client's old wood windows are badly in need of a new paint job. My client, a sailor, suggested using a high-performance polyurethane enamel boat paint on the windows to cut down on future maintenance. It seems to me that if a finish can adhere to the hull of a wooden boat, it should be able to perform well on a wooden window, but I've never used this paint in this application before. Is it a good idea?

A.Bill Feist, a former wood-finishes researcher with the Forest Products Laboratory in Madison, Wis., responds: Normally, I encourage people to use boat paints and varnishes for a number of nonmarine uses because of the general high quality of these finishes. But in this case, I think doing so might be a mistake.

Even though polyurethane enamels are made for many different surfaces on boats, polyurethanes in general are known for their brittleness — and enamels are even more brittle than flat or satin paints. This brittleness is okay where there is not a lot of wood movement. But an older wood window — especially the sill — is subject to considerable seasonal shrinking and swelling, which could result in premature cracking and peeling.

The best approach for weathered wood windows is to properly prep the substrate by removing all the old paint and carefully sanding the wood smooth, then cleaning with a detergent and bleach solution followed by a clear-water rinsing. When the wood has thoroughly dried, treat all of the bare surfaces with a paintable water-repellent preservative, such as Wolman's Woodlife Classic Clear Wood Preservative or Woodlife CopperCoat Green Wood Preservative (800/556-7737, www.wolman.com). Be sure to follow the manufacturer's specific directions for using these wood treatments.

After treatment, prime with a quality alkyd primer (I'd even consider using two coats), and top-coat with two coats of 100 percent acrylic satin latex house paint.